Endocrine-disrupting chemicals such as environmental estrogens contaminate our surroundings and impair the reproductive health of animals, and probably humans. These compounds may act as inappropriate estrogens, and/or interfere with the actions of endogenous estrogens, but their mechanisms of action at low, environmentally relevant concentrations are largely unknown. We have recently shown that signal cascades leading to induced functions initiated by estradiol (E2) at the plasma membrane are also potently initiated by nonphysiological estrogens (xenoestrogens). In cells that express a membraneform of the estrogen receptor-a (mERa), each xenoestrogen elicited unique signaling patterns (temporal, dose-response) via activation of extracellular-regulated kinases (ERKs) and/or calcium elevation. We will now address (1) the structural requirements for activating mERa to generate signals and their linked functions, by comparing the effects of alkylphenol xenoestrogens having varying carbon- chain lengths and structures, and prominent physiological estrogens (E2, estriol, and estrone);(2) active alkylphenols'ability of to act in combination with physiological estrogens via additive, synergistic, and antagonistic mechanisms;and (3) the G protein coupling of these responses. G proteins likely lie upstream of the signaling responses shown by our previous work and others'. We will now seek direct evidence for G protein subtype interactions with mERa via co-immunoprecipitation, use of specific inhibitors, and dominant-negative G protein subtype and decoy interaction peptide approaches. Changes in G protein coupling in response to both physiological estrogens and alkylphenol xenoestrogens will be examined. Our long-term objective is to use our established model system to answer a variety of detailed mechanistic questions about how specific structural features of different physiological estrogens and xenoestrogen subclasses affect actions through the nongenomic pathway and the mERa, and thereby disrupt endocrine processes. Health relevance: Knowing how environmental estrogens disrupt normal signaling and reproductive functions will enable design of new prevention and treatment strategies to deal with their toxicity. Demonstrating their low-dose effects will also guide re-evaluation of Federal regulations setting legal contamination limits for environmental estrogens. The extent and mechanisms by which environmental estrogens contribute to diseases of estrogen overexposure (eg.breast and pituitary cancers, infertility) must be understood so that exposures can be limited to safe levels.